The best place to start is the bottom, knowing that you know nothing. That lets you approach it with humility and openness.

I would recommend playing around with things in a virtual machine or getting some old hardware up and running using something super automatic like CasaOS and then getting a few wins out of that. Running on real hardware is good if you can just leave it running and have some basic services you can set up and play with. I would recommend getting Nextcloud up and running as a good start. Have fun!